Accurate operation of inverter packages or modules requires current sensing of the AC current to ensure effective system performance. AC current sensing is typically implemented using core-based magnetic sensors. Open-loop, core-based current sensors are limited in performance especially due to negative effects of the iron core. For example, open-loop, core-based current sensors suffer from hysteresis, saturation, non-linearity, temperature-dependent permeability, eddy current effects, etc. Some of the issues can be addressed using an external circuit for compensating the magnetic flux generated by the test current, and a probe for determining the zero-flux condition in the airgap. However, the additional circuitry, compensation winding and additional power dissipation in the compensation winding add significant cost to the overall sensing implementation.
In most cases, the intrinsic accuracy of core-based sensors is insufficient to meet end-customer requirements, e.g. for automotive traction inverters. Therefore, an end-of-line calibration may be required to compensate for gain and offset errors of the sensor. This calibration step is expensive since it requires to force high currents at high accuracy after the assembly of the inverter module and the current sensor. Since the calibration step is usually only performed at room temperature, the residual error due to lifetime drift and temperature dependency remains significant and impacts the overall system performance.
Thus, there is a need for an improved external power sensor for semiconductor modules.